So it seems like I can never find the answers I am looking for these days.

I am in the process of adding an enforcer wheel on my 07 FLHX, I have all the required hardware, going to send the wheel out for powder.

Question is I am running a Metzler ME880 on the front and rear and have been really happy with this tire.

Can I run a 120/70ZR19 ME880 on this wheel?

 

120/70ZR19 should fit without an issue...The tire will go on that 3.5" wide Enforcer. It will increase the overall diameter by approx 1/2" (decrease tire to fender clearance by 1/4"), but people are installing larger overall 21" wheel/tires without any or with minimal mods for tire clearance.

Are you going to run a "R" Radial in the Rear?

Typically it's accepted to be able to run a Bias Front / Radial Rear (in fact Harley does this on some models), but not the other way around